The present invention relates to a liquid crystal display device, and in particular to an active matrix type liquid crystal display device employing active elements such as thin film transistors.
The liquid crystal display devices are beginning to be widely used as display terminals of information processing equipment (office automation equipment) such as personal computers for their thinness, light weight and display quality comparable to that of cathode ray tubes.
The active matrix type liquid crystal display device has a plurality of nonlinear elements (active elements, switching elements) each associated with a respective one of a plurality of pixel electrodes arranged in a matrix. The liquid crystal at each pixel in the active matrix type liquid crystal display device is driven at all times in theory (i.e. with the duty ratio of 1.0), and consequently the active matrix type liquid crystal display device provides higher contrast ratio than the so-called simple matrix type liquid crystal display device employing time-multiplex driving, and the active matrix type driving is becoming indispensable especially for the color liquid crystal display device. One of representative active elements is a thin film transistor (TFT).
The active matrix type liquid crystal display device using thin film transistors is disclosed in Japanese Patent Application Laid-open Sho 63-309921 and xe2x80x9c12.5-inch diagonal active-matrix type color liquid crystal display employing a redundant configurationxe2x80x9d NIKKEI ELECTRONICS, pp. 193-210, Dec. 15, 1986, published by NIKKEI McGRAW-HILL Co., for example.
The liquid crystal display device (or the liquid crystal module) includes a liquid crystal display element (or a liquid crystal display panel, a LCD (Liquid Crystal Display device), a backlight disposed below the liquid crystal display element to serve as a planar lighting source for the liquid crystal display element, driving circuit boards disposed around the periphery of the liquid crystal display element, a plastic molded case for housing and holding therein the liquid crystal display element and the backlight, an upper metal shield case having a display window and housing the above-mentioned components and a lower metal shield case housing the above-mentioned components in cooperation with the upper metal shield case. The above-mentioned liquid crystal display element includes a pair of opposing and spaced insulating substrates made of material such as glass or plastic with transparent display electrodes and orientation films stacked thereon facing each other, a sealing member in the form of a rectangular peripheral frame for sealing the periphery of the two insulating substrates, liquid crystal material filled into the space between the two insulating substrates via a filling hole for the insertion of the liquid crystal material formed in the rectangular peripheral frame of the sealing member, and a pair of polarizers disposed below and above the liquid crystal display element for polarizing and analyzing light, respectively.
Liquid crystal display devices are manufactured using high manufacturing techniques in extremely dust-free environment, but a defective display called xe2x80x9ca line defectxe2x80x9d sometimes occurs which displays a line formed of pixels turned OFF or ON at all times on a display screen when a line among signal lines for display is broken.
Liquid crystal display elements having this line defect are screened out in the step of product inspection and are discarded, and consequently, the manufacturing yield rate of the liquid crystal elements is deteriorated and the production cost is increased. Consideration has been given to the need to repair the line defects.
FIG. 12 is a schematic plan view of a liquid crystal display element and driver circuit boards disposed around the periphery of the liquid crystal display element in a conventional liquid crystal display device.
Reference character LCD denotes a liquid crystal display element, SCR is a useful display area, GD are scanning signal drivers (driver ICs), GB is a scanning signal source circuit board, DD are video signal drivers (driver ICs), DB is a video signal source circuit board, CONT is a control circuit board, DATA are video signal lines, DAN is a point of a line open in one of the video signal lines DATA, DH is a line-open repair line, and CN1 and CN2 are first and second line-open repair connection points, respectively.
As shown in FIG. 12, a large number of video signal lines DATA are arranged in the useful display area SCR of the liquid crystal display device LCD. FIG. 12 illustrates that a line open occurred in one of the video signal lines DATA.
Video signals for display are supplied to the video signal lines DATA from the video signal drivers DD. But, if a point of the line open DAN occurs in one of the video signal lines DATA, the proper video signals can not be transferred downward from the point of the line open DAN in FIG. 12, and consequently, the above-explained defective display called the line defect occurs.
For eliminating the defective display caused by the line open, a conventional technique employs a U-shaped line-open repair line DH extending around the useful display area SCR on the liquid crystal display element LCD. With this configuration, if the point of the line open DAN occurs in the video signal line DATA, the video signal line DATA containing the point of the line open DAN is electrically connected to the line-open repair line DH by fusing the first and second line-open repair connection points by laser beam or the like so as to eliminate influence of the line open.
This conventional technique supplies the video signals to a portion of the video signal line DATA below the point of the line open DAN in FIG. 12 by first transferring the video signals to the line-open repair line DH via the first line-open repair connection point CN1 from the video signal driver DD and then to the portion of the video signal line DATA below the point of the line open DAN from the line-open repair line DH via the second line-open repair connection point CN2.
There is the following problem with this conventional technique.
It is necessary that the line-open repair line DH for transferring the video signals to the video signal line DATA containing a line open is disposed outside the useful display area SCR, and consequently, the route of the line-open repair line DH necessarily becomes long and therefore parasitic capacitance and resistance of the line-open repair line DH increases such that delay in the video signals is caused. That is to say, a difference of a time delay in the video signals is produced between the video signals supplied via the line-open repair line DH from the video signal driver DD because of its line open in the video signal line DATA and the video signals supplied directly from the video signal driver DD by the video signal line DATA having no line open. In a case where a uniformly gray image is displayed over the entire screen area, if the line-open repair line DH is used to repair a line open, a delicate difference in display brightness occurs forming a boundary on the point of the line open DAN, and deteriorates the quality of display compared with the liquid crystal display device having no points of the line open DAN.
It is an object of the present invention to provide a liquid crystal display device featuring a high quality display image and a high manufacturing yield by suppressing variations in brightness of the display screen due to delay in signals caused by repair of the line open in the signal lines.
To accomplish the above objects, in accordance with one embodiment of the present invention, there is provided a liquid crystal display device comprising: a pair of opposing substrates at least one of which is transparent; a liquid crystal layer sandwiched between the pair of opposing substrates; a plurality of scanning signal lines extending in a first direction on a surface of one of the pair of opposing substrates facing the liquid crystal layer and juxtaposed in a second direction transverse to the first direction; a plurality of video signal lines insulated from the plurality of scanning signal lines, extending in the second direction and arranged in the first direction; a plurality of pixel electrodes arranged in a matrix and each surrounded by two adjacent ones of the plurality of video signal lines and two adjacent ones of the plurality of scanning signal lines; a plurality of active elements each associated with one of the plurality of pixel electrodes, an output electrode thereof being connected to one of the plurality of pixel electrodes, a control electrode thereof being connected to one of the plurality of scanning signal lines and an input electrode thereof being connected to one of the plurality of video signal lines; a video signal line driver circuit disposed outside the matrix for supplying video signal voltages to each of the plurality of video signal lines; a scanning signal driver circuit disposed outside the matrix for supplying scanning signal voltages to each of the plurality of scanning signal lines; at least one line-open repair line extending near ends of one of (i) the plurality of scanning signal lines and (ii) the plurality of video signal lines opposite from output terminals of a corresponding one of (iii) the scanning signal driver circuit and (iv) the video signal driver circuit; the at least one line-open repair line being electrically connectable to an end of a signal line of a corresponding one of (i) the plurality of scanning signal lines and (ii) the plurality of video signal lines; and at least one signal amplifier connected to the at least one line-open repair line and being connectable to one of the output terminals of the corresponding one of (iii) the scanning signal driver circuit and (iv) the video signal driver circuit.
To accomplish the above objects, in accordance with another embodiment of the present invention, there is provided a liquid crystal display device comprising: a pair of opposing substrates at least one of which is transparent; a liquid crystal layer sandwiched between the pair of opposing substrates; a plurality of scanning signal lines extending in a first direction on a surface of one of the pair of opposing substrates facing the liquid crystal layer and juxtaposed in a second direction transverse to the first direction; a plurality of video signal lines insulated from the plurality of scanning signal lines, extending in the second direction and arranged in the first direction; a plurality of pixel electrodes arranged in a matrix and each surrounded by two adjacent ones of the plurality of video signal lines and two adjacent ones of the plurality of scanning signal lines; a plurality of active elements each associated with one of the plurality of pixel electrodes, an output electrode thereof being connected to one of the plurality of pixel electrodes, a control electrode thereof being connected to one of the plurality of scanning signal lines and an input electrode thereof being connected to one of the plurality of video signal lines; a video signal line driver circuit disposed outside the matrix for supplying video signal voltages to each of the plurality of video signal lines; a scanning signal driver circuit disposed outside the matrix for supplying scanning signal voltages to each of the plurality of scanning signal lines; at least one line-open repair line extending near ends of one of (i) the plurality of scanning signal lines and (ii) the plurality of video signal lines opposite from output terminals of a corresponding one of (iii) the scanning signal driver circuit and (iv) the video signal driver circuit; the at least one line-open repair line being electrically connectable to an end of a signal line of a corresponding one of (i) the plurality of scanning signal lines and (ii) the plurality of video signal lines; and the at least one line-open repair line being connected to an unused one of output terminals of driver ICs forming the corresponding one of (iii) the scanning signal driver circuit and (iv) the video signal driver circuit.
In the present invention, with the configuration having a signal amplifier connected to a line-open repair line, video signals to be transferred to a repaired video signal line via the repair line are amplified by the signal amplifier, and thereby a time delay of the video signals is reduced.
Also in the present invention, with the configuration in which a line-open repair line is connected to an unused one of signal output terminals of a driver IC disposed at an extreme end of the display screen which is not connected to any video signal lines, the required length of the line-open repair line is shortened and thereby a time delay of the video signals is reduced.
Usually, in both of these embodiments, each of the plurality of video signal lines is connected to pixels of the plurality of pixels arranged in a same column of the matrix via a respective one of the plurality of active elements, and each of the plurality of scanning signal lines is connected to the active elements associated with pixels of the plurality of pixels arranged in a same row of the matrix, usually. The at least one line-open repair line has at least one portion thereof which is disposed in a periphery of the one of the pair of the substrates and extends along the ends of either the plurality of the scanning signal lines or the plurality of the video signal lines juxtaposed in the periphery. The at least one portion of the at least one line-open repair line formed in this manner is extended on a side of the one of the pair of the substrates opposite to another side thereof at which input terminals of the plurality of the scanning signal lines or the plurality of the video signal lines for receiving signals from either the scanning signal driver circuit(s) or the plurality of the video signal driver circuit(s) are disposed. The at least one line-open repair line has another portion thereof which is extended along an extension direction of the at least one portion thereof disposed in the periphery of the one of the pair of the substrates. If the at least one portion is extended along the ends of the plurality of scanning signal lines, the another portion is disposed in another periphery of the one of the pair of the substrates and extends along the ends of the plurality of the video signal lines juxtaposed in the periphery, or is disposed on a circuit board on which the video signal driver circuit is mounted. In the latter case, the another portion may be disposed inside of the circuit board, when the circuit board has a multilayered structure.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.